Chemical deposition of metallic films



Patented July 17, 1951 CHEMICAL DEPOSITION OF METALLIC FILMS LeopoldPessel, Philadelphia,

Pa., assignor to Radio Corporation oi America, a corporation of DelawareNo Drawing. Application July 30, 1948, Serial No. 41,721

11 Claims. 117130) This invention relates to the chemical deposition ofmetallic films on metal surfaces by simple immersion without the use ofelectrical current.

More particularly, the invention relates to improvements in the chemicaldeposition of metallic films in general, using a depositing solutionwhich includes pentanedione-2,4.

The chemical deposition of a metal upon another metal anodi-c thereto isvery old in the chemical art. It is a general principle that a metalwill replace from solution any other metal below it in the well-known.electromotive series. In general, however, the deposit of metal soformed is soft and spongy and usually may easily be rubbed off. In thepast, in order to get a hard, brilliant coating of metal on anothermetal, it has usually been necessary to deposit the metalelectrolytically.

The essence of the present invention lies in the discovery that when acertain organic chemical, namely; pentanedione-2,4, is included in asolution of a metallic salt, the metal will not only deposit morereadily on baser metals but will form deposits which, in hardness andbrightness, compare favorably with those produced by electrodepo'sition.

One object of the present invention is to provide an improved method ofdepositing metals chemically on other metals without the use of anelectric current.

Another object of the invention is to provide improved compositions forthe chemical deposition of metals.

Another object is to provide improved compositions for chemicaldeposition of metals, which compositions include pentanedione-2,4.

Another object of the present invention is to provide improvedcompositions for chemically depositing metals on baser metals, whichcompositions contain pentanedione-2,4, Water and a mutual solvent forpentanedione-2,4 and Water.

Still another object of the present invention is to provide improvedcompositions for chemically depositing a metal on another metal anodicthereto, which compositions contain pentanedime-2,4, water and an acid.

These and other objects will be more readily apparent and the inventionwill be better understood from the following specification.

In general, the objects of the present invention are accomplished byfirst providing a solution comprising pentanedione-2,4, at least a smallamount of water, and a soluble metal compound. Next, the base metal tobe coated is preferably immersed in the above solution and allowed toremain until a coating of desired thickness is formed. Preferably, themetal which is to be deposited should be cathodic toward the base metalupon which deposition is to occur, al-

though examples have been found in which, this so requirement is notnecessary. The metal compound which is in solution forms a complex saltwith the pentanedione-2,4. In some cases, it appears that the depositionwhich occurs is due simply to the preference of the pentanedione-2,4radical for one metal over another one, resulting in the deposition ofthe latter as a film on the surface of the immersed metallic body.

Although it is preferred to immerse the base metal being coated in asolution of the metal which is being deposited, the base metal may besubjected to the action of the metal being deposited in other ways. Forexample, a plate of the base metal may simply be covered on one side.:with a layer of thesolution or the solution may be sprayed over thesurface of the base metal.

One of the necessary requirements for proper deposition of a metallicfilm, according to the invention, is the presence of at least a smallamount of water. Without water, if a film is deposited at all,deposition occurs at an extremely slow rate. The presence of as littleas 0.5 percent by volume of water causes a very noticeable accelerationof film formation, which becomes increasingly more pronounced as thepercentage of water increases. Most metals are deposited at. roomtemperature in a matter of seconds if 1 to 2 percent by volume of wateris present. The amount of water may be increased up to its maximummiscibility with pentanedione-2,4 without separating into two phases.Still more water may then be added by including a mutual solvent forpentanedione-2,4 and water, such as diacetone alcohol. At roomtemperatures, and using a mutual solvent, as much as 25 parts by volumeof water may be mixed with 50 parts of pentanedione-2,4. This proportionmay be increased by raising the temperature. A preferred solvent mixturecontains 50 volume percent pentanedione-2,4, 25 volume percent water and.25 volume percent diacetone alcohol. Other mutual solvents such asacetone and gamma valero lactone may also be employed in somewhatsmaller amounts.

Examples of the manner in which the present invention may be practisedin the case of specific metals will now be given:

EXAMPLE I Deposition of copper on iron or steel An aqueous solutioncontaining 7 percent by weight of cupric sulfate is added to from 10 to30 percent by volume of pentanedione-2,4. In this solution is immersed apreviously cleaned piece of iron or steel. A hard, brilliant copper filmforms on the base metal in a matter of seconds. The adhesion is so goodthat it is almost impossible to remove the coating by rubbing.

- per hydroxide until vent mixture is not I ratio is l gram of coppervoi! solvent mixture. A piece mersed in this mixture'becomes coatedwithinroom temperature, with a. Y brilliant film of metallic copperhaving such adhesion that it cannot be rubbed on. The density andsuperior adhesion of this film'is" such an excellent stop-of!" to-prevent carbon penetration in carburizing operations. Anotherapplication is in the copperto seconds, at

above examples is solely 'tion of the componen "film, particularly 7 ofwhen the same method'is carried out without adding pentanedione 2,4,-the red copperdeposit which is formedis not only-dullbut is spongy andshows pooradhesion to ExAMPnEn Deposition. o .ama 5,,,,, u

the metal surface.

Another preferred method of preparing a solution, for thedeposition oicopper. comprises shaking a mixture I v pentanedione-zA, v volumepercent water and 25 volume percent diacetone alcohol with cop saturatedwith the copper compound.- Although the proportion of copper at allcriticaL'one preferred of iron or steel imthat it may serve as platingof powdered iron cores used in the radio industry.

The function of the diacetone alcohol in the that 01' maintaining ahomogeneous solution of water and pentanedione-2,4 at room temperaturewithout separa- Any other solvent mutually compatible with water andpentanedione- 2,4 may be used or such solvent may be left out entirelyif the water content in the mixture is to be kept low.

' The film-forming ability of the above-described copper compounds maybe accelerated by additions of moderate amounts of acids. Excessive acidadditions cause deterioration of the its adhesive properties. Thus,additions of concentrated formic acid up -to 20 percent, acceleratedfilm' formation without affecting adhesion ofthe metal films. Additionsbeyond 20, percent containing 1 50 volume. percent hydroxide tothesolhydroxide to 20 cc.-

the solution is thoroughly i on steel or zinc.

ausedthe progressive deterioration of adhesion of the film to the base.

YAddition of concentrated hydrochloric acid up to 5 percent by volume I'film formation. Additions beyond 5 percent by caused acceleration. of

volume caused progressive inhibition offilrn deposition.' The eil'ect ofother acids was similar, except that the maximum volume additioncompatible with good film properties acid.

Although, in the previously described examples, iron or-steel wasspecified as the base, copper may be deposited. also] on other metalsurfaces in accordance with, the present invention.

Some examples. of other metals are zinc, lead, lead-tin alloys,aluminum, iron alloys contain-j ing nickel,- silicon, manganese, etc.vflhe'base" metal may be any metal' to which copper is cathodic,

It is also possible todeposit flms'oi many other metals, it beingnecessary only that, in general, the metal to be depositedbe cathodic tothe base metal upon which the deposition is to occur.

Examples of the deposition of other metals follow:

EXAMPLE III Deposition of silver on copper A mixture comprisingpntanedione-ZA,

varied with the adherent filmpt metallic. silver;

. volume percent, and.

rated with silver oxide. A' sheetoi copp immersed in this solution witha shiny,

. fle i lf Me l To a mixture'icontaininz pehtanedione-ZQ, 90 water, 10volume- :percent, weight oi-palladium chloimmersed in this, soluis'added1 percent by ride. A sheet of copper ,tion iscoated with' ,a.shinyadherentfilm of palladium metal.

7 Deposition offacid'on steelyetc. I To a mixture containingpenta'nedione-ZA, 50 volume :percent, water," ,25 volume. percent, anddiacetone alcohol, 25 volume percent, ,isadded 5 volume} percent oi asaturated-aqueous acid gold chloride solution. .A gold of; good qualityis deposited. on any of the, variousmetals more active thangold.immersed in this solution. Forexample. a shiny gold film is deposited Agold film oi somewhat less shiny appearance is obtained on immersingsilver. A gold film may also be deposited on aluminum by adjusting thepH of the solution to about 6 by the addition-of an alkali such asammonia. The film whi h is deposited on aluminum is dark at first butmay be buffed to the characteristic shiny gold color. Its adhesion isvery good.

EXAMPLE VI Deposition of nickel on steel A solution of pentanedione-2,4,50 volume percent, water, 25 volume percent, and diacetone alcohol, 25volume percent, was saturated with nickel hydroxide. A thin film ofnickel is deposited on cold-rolled SAE 1010 steel immersed in thesolution.

- Deposition s lbismutni 0 7i. 5 and steel containing pentanedione-2A,50 volume percent, water, 255volume percent,"and diacetone alcohol, 25vol e rated with bismuth oxide. of bismuth metal were obtained byimmersing'pieces of various other metals, such as zinc and steel, inthis solution. EXAMPLE VIII Deposition of lead on zinc The same solventmixture in Example VII was saturated with lead oxide '(PbO). From thissolution, films of metallic lead were obtained onpieces oi immersedmetal, suchas "Deposition of ctuimium on'einc,

The same solvent mixture used in Example VII was saturated with cadmiumoxide. Ex-

tremely thin films of cadmium were deposited trom this solution on othermetals such as zinc.

EXAMPLE x Deposition of platinum on copper and steel To the same solventmixture used in Example VII, 10 volume percent of a 5' percent aqueouspercent, was satuplatinum chloride solution was added. A sheet of copperimmersed in this solution was coated with a shiny film of platinum,which, although somewhat dark in color, showed excellent adhesion. Thisfilm formed very slowly, requiring several hours at room temperature. Asimilar film of platinum was also obtained on steel.

EXAMPLE XI Deposition of selenium on copper, etc.

Solutions made according to the present invention may also be used toprecipitate a film of metallic selenium on some immersed metals. As oneexample, a 1 percent (by weight) solution of HzSeOa was added to thesolvent mixture containing pentanedione-2,4, 50 volume percent. water,25 volume percent, and diacetone alcohol, 25 volume percent. A copper orbrass sheet, immersed in this solution, at room temperature, is rapidlycoated with a film of selenium which is first purple, then blue, and,lastly. gray. The film is of brilliant smoothness and shows excellentadhesion. A sheet of iron or carbon steel, such as annealed springsteel, immersed in this solution, becomes also coated with a black,shiny, adherent film of selenium, but the formation in this case is muchslower, requiring 4 to 6 hours, at room temperature. A strip of zincimmersed in solution becomes rapidly coated with a brown, smooth,adherent film of selenium. On magnesium, a reddish-brown film ofselenium is obtained. The formation of a selenium film on steel may bebrought about more rapidly by first copper plating the steel, asdescribed in Examples I or II, and then immersing the plated steel in aseleniumcontaining solution which includes pentanedione- 2,4. A rapidconversion of the copper film into a selenium film takes place. Metalscoated with selenium, in this manner, may be used in apparatus such asrectifiers, photoelectric cells, etc. Instead of selenious acid, asolution of selenium oxychloride, or some other soluble compound ofselenium may be used.

EXAMPLE XII Deposition of tellurium on zinc or steel A saturatedpotassium tellurate solution in water was prepared and acidified withconcentrated hydrochloric acid to a pH of 4. 10 percent by volume or theresulting solution was added to the solvent mixture described in ExampleVII. Pieces of zinc or steel, immersed in this solution. were rapidlycoated with films of tellurium.

The above examples are intended to be merely illustrative of the manypossible combinations of film and base material which may be carried outby utilizing the present invention. As is the case with chemicalreactions in general, the reactions occurring in the above describedexamples may be accelerated by increasing the temperature or byagitation of the solution, or by adjustment of the pH, all in accordancewith the principles well known in this art. It has beentound that thecomplex salt which is formed between the metal and the pentanedione-2,4,especially in the presence of water or acids, provides an improvedmethod of plating immersed metal surfaces with smooth, often brilliantand well-adhering films of metal, without the use of electrical current.even in those cases where the precipitation of the corresponding metal,without the use of pentanedione-2,4, ordinarily results in a loose,sponsy deposit with poor adhesion.

I claim as my invention:

1. In a process 01' chemically depositing a film of metal on a body ofanother metal anodic thereto by subjecting said body to a solution of awin-- ble compound of said metal to be deposited until said film hasassumed a desired thickness, the improvement consisting in utilizing asthe solvent portion of said solution a mixture comprisingpentanedione-2,4 and water, said water being present in said mixture ina proportion between 0.5 volume percent and the upper limit ofmiscibility with said pentanedione-2,4.

2. A process according to claim I in which said solvent portion alsoincludes a mutual solvent for pentanedione-2,4 and water.

3. A process according to claim 1 in which said solvent portion alsoincludes a relatively small volume percentage 01' an acid.

4. A process according to claim metal to be deposited is copper.

5. A process according to claim 1 in which the metal to be deposited issilver.

6. A process according to claim 1 in which the metal to be deposited isselenium.

7. A process according to claim 1 in which said metal body consistsessentially or iron. I

8. A process according to claim 1 in which said metal body consistsessentially of an iron-carbon alloy.

9. A process according to claim 1 in which said metal body comprisescopper.

10. A composition for chemically depositing a metal on another metalanodic thereto comprising pentanedione-2,4, water and a soluble compoundof the metal to be deposited, the water being present in a proportionbetween 0.5 volume percent and the upper limit of miscibility withmaturedime-2,4.

11. A composition according to claim 10 ineluding also a minorpercentage of acid.

LliOPOID REFERENCES CITED The following references are oi record in thetile 0! this patent: I

' UNITED STATE8 PATIN'I'B Number Name Date 2,351,974 Kollmar June 20.1044 2,430,520 Marboe Nov. 11, 1047 l in which th

